Fatigue is described as a major complaint in patients undergoing chemotherapy. Yet it is unknown whether the fatigue has any relationship to the quality or quantity of sleep or to the sleep/wake circadian rhythm cycle. One of the easiest circadian rhythms to measure is sleep/wake activity. Sleep may also play an important role in the quality of life of these patients. If patients with synchronized rhythms show better tolerance to treatment, then synchronizing the rhythms with light therapy before the start of therapy would be encouraged. Before treatment studies or synchronization studies can be implemented however, more understanding is needed about the relationship between fatigue and sleep, about the normal circadian rhythms in cancer patients and what happens to rhythms during traditional therapy. Current technology allows for non-invasive, ambulatory measurements of circadian rhythms and sleep/wake activity. We propose to study sleep/wake activity cycles in outpatients with breast cancer to examine the relationship between fatigue experienced during the day with sleep/wake cycles and with the quality and quantity of sleep recorded at night; to examine the effect of fatigue and desynchronized sleep/wake rhythms on quality of life and mood (e.g., depression) during multiple cycles of treatment; to examine whether sleep/wake rhythms influence a patient's tolerance to treatment; to examine the effect of chemotherapy on sleep/wake rhythms and quality and quantity of sleep, over the time course of multiple cycles of chemotherapy; to examine the relationship between light exposure and circadian rhythms. This will be accomplished by placing Actillumes on patients for 72-hour periods each week of cycle one and cycle four of chemotherapy. At each visit questionnaires evaluating sleep, fatigue, depression and quality of life will be administered. In addition, since many of these women will be older, each woman will have a complete polysomnogram to rule out sleep disordered breathing and periodic limb movements in sleep. Results will provide a scientific basis for future intervention studies, particularly studies with light therapy which can re-synchronize rhythms.